| From: | Jim Nasby <Jim(dot)Nasby(at)BlueTreble(dot)com> |
|---|---|
| To: | Amit Kapila <amit(dot)kapila16(at)gmail(dot)com>, Andres Freund <andres(at)anarazel(dot)de> |
| Cc: | David Steele <david(at)pgmasters(dot)net>, Robert Haas <robertmhaas(at)gmail(dot)com>, Thom Brown <thom(at)linux(dot)com>, Simon Riggs <simon(at)2ndquadrant(dot)com>, Jesper Pedersen <jesper(dot)pedersen(at)redhat(dot)com>, pgsql-hackers <pgsql-hackers(at)postgresql(dot)org> |
| Subject: | Re: Speed up Clog Access by increasing CLOG buffers |
| Date: | 2016-03-23 03:21:19 |
| Message-ID: | 56F20BAF.10803@BlueTreble.com |
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| Lists: | pgsql-hackers |
On 3/22/16 9:36 AM, Amit Kapila wrote:
> > > Note, that we are doing it only when a transaction has less than
> equal to
> > > 64 sub transactions.
> >
> > So?
> >
>
> They should fall on one page, unless they are heavily interleaved as
> pointed by you. I think either subtransactions are present or not, this
> patch won't help for bigger transactions.
FWIW, the use case that comes to mind here is the "upsert" example in
the docs. AFAIK that's going to create a subtransaction every time it's
called, regardless if whether it performs actual DML. I've used that in
places that would probably have moderately high concurrency, and I
suspect I'm not alone in that.
That said, it wouldn't surprise me if plpgsql overhead swamps an effect
this patch has, so perhaps it's a moot point.
--
Jim Nasby, Data Architect, Blue Treble Consulting, Austin TX
Experts in Analytics, Data Architecture and PostgreSQL
Data in Trouble? Get it in Treble! http://BlueTreble.com
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